The porous endocardial electrode.

The permanent endocardial electrode has exhibited the problems of dislodgement, excessive threshold rises and loss of sensing. These failure modes are addressed with a new electrode incorporating a porous body of Pt-Ir fibers with a fiber diameter of 20 micrometers and an overall density of 10%. Porous electrodes have the advantages of utilizing the electrode interior both for tissue ingrowth to improve anchoring and for electrolyte penetration which improves R wave amplitude and reduces polarization losses. A series of 20 porous electrodes was compared with 17 solid electrodes of similar dimension. Electrodes were implanted in dogs in the apex of the right ventricle, and were subsequently followed up to 210 days. Comparison of the electrode data revealed that the porous electrodes had a 40% reduction in chronic voltage thresholds and had an overall dislodgement rate of 10%, compared to 53% for the solid electrodes. Histological examination revealed tissue ingrowth throughout the electrode interior and a fibrotic capsule about half the thickness of the solid electrodes. R wave stability was enhanced with the porous electrode due to improved anchoring, reduction in slew rate changes and less R wave attenuation. Assuming results are translatable to humans, the porous electrode will provide a greater pacing safety margin when used with a standard demand pacemaker, or improved longevity with the same safety margin as solid electrodes if used with a programmable pacemaker. The incidence of dislodgement and sensing failure will also be diminished with the porous electrode.